Mr Ilhan is charged with making propaganda for the banned Kurdistan Workers' Party (PKK) and with taking part in an illegal organisation. Mr Ilhan, a bazaar porter from the city of Mersin, denies the charges.
Using sign language at a hearing in the south-eastern city of Adana, he said he had got caught up in a violent pro-Kurdish demonstration. Under Turkey's anti-terrorism law it is an offence to show any sign of support for the PKK.
Turkey's judiciary often administers harsh penalties on bafflingly slight evidence. However, even by Turkish standards, this case is extraordinary. If Mr Ilhan is found guilty, the court is expected to pass a sentence close to the 25 years that the prosecutor has asked for.
